Transition-metal-directed assembly of well-defined organic architectures possessing large voids: From macrocycles to [2]catenanes

This paper discloses coordination approaches to well-defined organic structures including macrocycles, a three-dimensional cage-like compound, and [2] catenanes. These supramolecules self-assembled from (en)Pd(NO3)(2) (1, en = ethylenediamine) and appropriate polypyridyl-substituted ligands, Treatment of 1 with 4,4'-bipyridine (2), for example, gave the macrocyclic tetranuclear Pd(II) complex [(en)Pd(mu-2)](4)(NO3)(8) quantitatively, while macrocyclic dinuclear Pd(II) complexes were assembled from 1 and flexible ligands such as PyCH(2)CH(2)Py (Py = 4-pyridyl). From the tridentate ligand 1,3,5-(PyCH(2))(3)C6H3 and 1 in 2:3 ratio, however, a three-dimensional cage-like compound was assembled in high yields only in the presence of certain types of guest molecules, providing an entire model for 'induced-fit.' The coordination approach made it possible to interlock two apparently continuous molecular rings: i.e. a macrocycle assembled from 1 and 1,4-(PyCH(2))(2)C6H4 was found to exist in equilibrium with its catenated dimer, and a polar medium strongly pushed the equilibrium toward the catenane up to a greater than 99:1 ratio.